1. Field of the Invention
This invention relates to exposure systems using a scanner, more particularly to those systems having a transport system.
2. Background of the Invention
Traditional photofinishing systems use a scanning system to transfer the images to photographic paper. The scanning system typically writes a line or pixel of an image at a time. A transport system then moves the paper or other substrate and the scanning system writes the next line. However, the scanning system and the transport system currently operate independently from each other. This can cause artifacts in the image.
The most common artifact is what is referred to as xe2x80x98banding.xe2x80x99 This is caused by position misplacement where position of the completed image has unintended bands of colors or shades of gray. Individual lines or pixel components of the image have not been placed onto the substrate in the proper position relative to previously placed lines or pixel components of the image. This creates undesired color and or intensity variations know as motion artifact banding. Assembly of a competed image requires the accurate position placement of each of the line or pixel components, which can represent different colors and intensities, to produce the final desired image. The repetition of the line or pixel components should occur at the same place on the substrate, but do not necessarily have to occur at the same time. This inaccuracy of position overlap, not the time lapse between the number of times unique line or pixel components are imaged onto the substrate, causes the banding artifact if the registration between the line or pixel components is not accurate.
Image registration fails when the motion of the scanner does not match the motion of the transport system. The human eye detects the banding artifacts most readily when at a spatial frequency of 0.05 cycle/mm to 1 cycle/mm. These are spatial frequency errors that occur due to some disturbance of the motion of the substrate at some frequency.
For example, a disturbance unique to the substrate and not the scanner, which occurs at 10 Hz, or 10 times every second, translates into a 0.05 cycle/mm spatial banding artifact in the image for a system having a speed of 8 inch/sec. The calculation is as follows:                     10        ⁢                  xe2x80x83                ⁢        cycles            sec        *                  1        ⁢                  xe2x80x83                ⁢        sec                    8        ⁢                  xe2x80x83                ⁢        inches              *                  1        ⁢                  xe2x80x83                ⁢        inch                    25.4        ⁢                  xe2x80x83                ⁢        mm              =            .05      ⁢              xe2x80x83            ⁢      cycles        mm  
These types of banding artifacts typically result from both DC speed inaccuracies associated with independent control of the transport system and the scanner. Control of each of these systems can have unique DC and AC position and speed errors due to many factors such as mechanical tolerances associated with the feedback transducer, errors in the feedback transducers, errors in the motors (cogging or torque ripple), and errors in drive train tolerances.
Therefore, a method is needed that allows the rate of the scanning system and the transport system for image exposure systems to be more closely coupled to eliminate image artifacts such as banding.
One aspect of the invention is a photofinishing system that coordinates movement of an image created by a spatial light modulator and movement of the substrate upon which that image is to be imaged. The system has a transport S system for moving the substrate, with an encoder wheel attached to the carrier in the transport system. The encoder wheel generates a signal dependent upon the position of the carrier. A second encoder is attached to the drive motor of the transport system and produces a second signal dependent upon the control of the drive circuit. Two separate circuits are used to monitor and adjust operation of the system based upon these signals.
It is an advantage of the invention in that it produces higher quality images with no banding artifacts.
It is a further advantage of the invention in that either one of the two circuits can be used to improve image quality, or they can be used simultaneously.